As an advantageous method for producing a multi-layer foamed sheet consisting of a structure having plural layers, a coextrusion method is proposed wherein resin materials corresponding to respective layers are plasticized and melted using plural extruders and then molten resins supplied from respective extruders are laminated and integrated in a die with each upon extruded out of a die.
Japanese Unexamined Patent Publication No. 7-16971 discloses that an unevenness in the widthwise thickness of each layer can be improved by performing a coextrusion T die foaming procedure while adjusting the fluidity of a polyolefinic resin layer (A) at a level similar to that of a foaming polyolefinic resin layer (B) upon the coextrusion.
Such unevenness in the thickness is a drawback experienced frequently in a feed-block T die coextrusion procedure We made an effort in searching for a method for producing a multi-layer foamed sheet by a multi-layer circular die coextrusion method, and discovered that, in the multi-layer circular die coextrusion method generally employing a multi-manifold system, poor appearance is observed rather as a pattern of scales having diameters of several centimeters rather than as a wide-ranged drawback such as described above. An object of the invention is to provide a method for producing a multi-layer foamed sheet whose scale-like poor appearance is improved by means of a multi-layer circular die coextrusion method.